The present application relates to manufacture of integrated circuits and multichip modules, and more particularly to metal plating.
Note that the points discussed below may reflect the hindsight gained from the disclosed inventions, and are not necessarily admitted to be prior art.
Standard practices in plating include pre-plate surface preparations using solvents, acids, abrasives, surfactants, ultrasonic agitation, and vacuum plasma processes to remove organic contamination and surface oxidation of the substrate to be plated. Each of these surface preparation processes has distinct disadvantages such as toxic waste disposal, chemical damage to exposed surfaces of the substrate, mechanical damage to the substrate surface or other sensitive structures of the substrate composition, introduction of foreign particles to the surface, required rinsing of the surface after treatment and before plating, contamination of the plating bath from residues of these surface treatment methods, etc.
What is needed is a rapid and environmentally-friendly method of preparing surfaces for plating which leaves the surface in a pristine and optimal surface state for the subsequent plating process, and does not mechanically and/or chemically disturb sensitive substrates, and requires no rinsing of surface preparation materials, and does not contaminate the plating bath.
Additionally, many plating operations are carried out using surface masking techniques to provide a patterned deposition of the plated material. The mechanical and chemical compatibilities of the masking materials often place additional constraints on the types of surface preparation that can be performed before the plating process commences. For example, use of photoresist to pattern a plating substrate precludes the use of certain solvents to remove residual organic contamination from the exposed substrate plating base. Conventionally, to overcome this limitation, a vacuum plasma treatment (often referred to as “oxygen ashing”) employs oxygen ions and atomic bombardment to remove organic residues on the exposed plating base. However, this technique has disadvantages such as:
1. Slow, batch-type throughput limitation,
2. Critical line dimensions of the photoresist pattern are often changed by the oxygen treatment,
3. Thickness of the photoresist is decreased by the oxygen treatment.
4. Oxygen treatment reacts with the exposed plating base surface and grows additional oxides which inhibit the initiation of the plating process and lead to plating non-uniformities.
Also any masking materials, such as photoresist, are hydrophobic and tend to inhibit the flow of plating bath solutions into fine geometries. This can result in a defect known as “skip plating” where small, isolated openings in the photoresist simply do not plate up at all, or begin to plate later than do more open, exposed geometries. What is needed is a surface preparation prior to plating of patterned substrates which does not substantially disturb the patterning medium mechanically or chemically or dimensionally, and also promotes excellent wetting of aqueous solutions to the patterning medium so that the finest patterned geometries can be plated without “skip”.
The present application teaches new ways to perform plating in the manufacture of integrated circuits and multichip modules.